The Pediatric GI program at Children's Hospital (CH) and Massachusetts General Hospital (MGH) is dedicated to the preparation of academic investigators to a career in GI biomedical research. This program continues to build on its outstanding past experience in establishing productive and committed investigators. Fundamental features of the post-doctoral training format, the major component of this program, include direct research participation in conjunction with a comprehensive program of didactic instruction and enrichment activities to provide a deep foundation in biomedical science and modern research techniques. In addition, a new pre-doctoral laboratory research program is proposed to attract graduate students from the Division of Medical Sciences at Harvard Medical School (HMS) to choose careers in GI research. (A) Research Areas and Disciplines. The majority of trainees will undertake training in laboratory research in which emphasis is placed on the application of tools of molecular biology to GI research. Training is offered in several disciplines: Molecular Biology, Developmental Biology, Genetics and Immunology. These disciplines are applied to four research themes central to the current study of digestive diseases. For the few trainees undertaking training in clinical investigation, a rigorous preparation in relevant quantitative sciences, including Biostatistics and Epidemiology, is provided: (B) Level of Training, Background and Numbers of Trainees. This renewal proposes both post-doctoral and pre-doctoral training. Post-doctoral training is offered in individuals holding M.D.-Ph.D. degrees. Six post- doctoral positions are requested: three post-doctoral fellows will begin training each year, and remain in research training for a minimum of two years supported by this award. In addition, two positions are requested to initiate a new pre-doctoral program for outstanding graduate students at Harvard Medical School completing an undergraduate degree or enrolled in medical school. C) Training Facilities. Research training will take place in the existing laboratories of the research mentors; a group of established investigators with extensive existing interactions at M.I.T, Harvard Medical School and HSPH. Laboratories are present at MGH-East and in the Enders Research Building at CH. Didactic educational program will include those offered through the Harvard Medical School, the Harvard School of Public Health, Harvard University and M.I.T.